Enhanced adsorption and degradation of antibiotics by doping corncob biochar/PMS with heteroatoms at different preparation temperatures: Mechanism, pathway, and relative contribution of reactive oxygen species

Antibiotics in the water environment pose harm to animals, plants, and humans. In this study, biochar doped with sulfur (S), nitrogen (N), and NS was used to adsorb and activate peroxymonosulfate (PMS) to degrade the antibiotics chlortetracycline, ofloxacin, and sulfadiazine in an aqueous solution. The adsorption capacity of the biochar doped with single atoms increased significantly, and the maximum saturated adsorption capacities of undoped, N-doped, S-doped, and NS-doped biochar were 40.7, 85.5, 63.3, and 40.7 mg/g, respectively. The increase in specific surface area and the number of functional groups was the main cause for the increase in the adsorption capacity of heteroatom-doped biochar. The antibiotic degradation process involved the use of biochar to activate PMS and produce reactive oxygen species (ROS) for complete removal. The concentration of environmentally persistent free radicals (EPFRs) increased in response to heteroatom-doped biochar, and the type of EPFRs changed, which enhanced the ability of biochar to degrade antibiotics. At the 500 °C preparation temperature, the degradation rates of antibiotics by the undoped, N-doped, S-doped, and NS-doped biochar were 73.83%, 84.32%, 79.60%, and 74.10%, respectively, whereas the degradation rates at 900 °C were 82.38%, 93.78%, 91.11%, and 81.55%, respectively. The sulfate radical was produced during the activation process and made the largest relative ROS contribution to the increased adsorption capacity, followed by singlet oxygen, hydroxyl radical, and superoxide radical. Recycling experiments confirmed that the heteroatom-doped biochar was highly reusable and that the removal rates of N-doped biochar and S-doped biochar were high (81.94% and 78.06%, respectively).